Method of impregnating wood with paraffin wax and with polyethylene glycol to improve its cutting qualities



United States Patent O METHOD OF IMPREGNA'I'ING WOOD WITH PAR- AFFIN WAX AND WITH POLYETHYLENE GLY- COL TO `llVIPROVE- ITS CUTTING QUALITIES 6 claims.: (Cl. 117-149) This invention relates to a method for altering the 'cutting qualities ofwood, to render it easier to process with saws, planers and other wood cutting tools.` It relates in particular to the treatment of wood having wide natural differences in the cutting characteristics of the spring andsuinmerwood, to equalize `those properties and to make the wood substantially uniform in its behavior under the action of a knife or other cutter. It relates especially to such treatment for improving the cutting qualities of incense cedar pencilwood, and to the improved products. e

The invention is not limited to use in the pencil industry, but there are problems in that industry which are of such importance that the treatment to'be described herein would be fully justified even if no other use were found for it;A Hence, an understanding of the pencilwood problem is desirable, and a description of the new treatment and of its effects on pencilwood will necessarily show the-manner in which the same desired results `may be obtained in other woods or wood products.

t Wood cased pencils have been items of commerce for so l long that the `consuming public considers the qualities of the old standard product to be essential to a good pencil.

`Among the qualities as to which acceptance standards -have been established vthrough long usage are the density -and whittling properties of the wood, freedom fromprotruding grains at the cut surface after sharpening, and the color of vthe/freshly cut wood. The pencil manufacturer naturally` desires to keep his product within the informal tolerance limits imposed by tradition, and, additionally,

desires to use a wood which is easy to cut and which is suiciently `uniform to keep to a minimum the number of substandard pencils which must be rejected. Amongthe causes for rejection are warping, excessive softness, excessiv'e brittleness, `raised grain and failure of paint or lacquer to adhere.

'I'he standard acceptable pencil, both from the viewpoint of ease of `manufacture and from that of customer acceptance, has been made for over 100 years from easternred cedar, Junperus vrginana, grown principally in the Tennessee region of the United States. This remarkable wood is straight grained, red to brown in color, and hasuniform cutting `qualities `because of very little difference between `the hardness and density of its spring and summerwood. When cut or whittled with a knife, red

cedar pencilwood gives coherent curled shavings, rather than brittle` straight ones. `It has a natural lubricity which `appears `to be lacking in `the Vonly substitute pencilwoods located to date.` The need for a substitute wood has long been anticipated, however, and has become acute due to the depletion of first growth eastern red cedar and to the very inferior properties of second growth wood of this species. The latter is not straight-grained and is not uniform and cannot be used in making wood cased pencils.

Two woods have been found which have enough of the desired properties to make their use` practical in `pencil manufacture,` but each of them has defects t which must ICC be overcome if thel pencils made from them are to be of high quality which has become standard.. These woods are the western incense cedar, Libocedrus decurrens, west of the Rocky Mountains, and Kenya cedar, Junperus proc'era, grown in and near Kenya Colony in East Equatorial Africa. i l The western incense cedar is relatively free from the warping tendencies of Kenya cedar, but it presentsother problems to the pencil manufacturer andpencilsmade from it, in its natural state, are of variable quality. tIts light color is altered easily by staining to give it a `color resemblance to eastern red cedar. Others of its propcrties are altered less easily. The difference in density between the spring wood and the summerwood of western incense cedar leads to serious problems, as it does not cut or whittle uniformly. The softerportions tend to be compressed by the cutting edge and thereafter `to` tear. In consequence, rough splinter ends are found on the cut surfaces. The denser layers offer temporary resistanco to a cutter, requiring application of more force than when cutting the spring wood, and then, when thel blade passes through the resistant summer wood it tends "to lunge forward under the added force, thereby tearing the next layer of spring wood. The cuttings are not the desired coherent curls, due to the described non-uniformity. The spring wood requires stiffening and both the spring and summer woods require lubrication.'

Keeping in mind the demand for pencils of uniformly high quality, an important economic problem is presented `by western incense cedar. There is-a great differencev in the several significant properties betweenthe sapwood and the heartwood of this tree and pencil makers have gone to the extreme of using one or the otherof these and of discarding the other. Because of these differences in properties, it has become a necessary but expensive procedure to inspect every individual pencil slat made from western red cedar and to classify the slats into three or more grades. Only the top grades have been deemed useful for making acceptable quality pencils, and the waste has been appalling. Of the wood used, aboutSO percent is lost as sawdust, 45 percent has been culled out as useless and only 25 percent has been useful for pencil slats, and of these, less than one-third are of thegdesired top` grade in their natural state.

Attempts have been made in the -past to overcome the above-outlined diliiculties, with varying degrees of partial success. So far as is known to the worlds largest pencil manufacturers and to their suppliers of pencilwoodv slats, no previously proposed treatment hasmade it possible to reproduce consistently the quality of the best grade of eastern red cedar pencils when using Kenya cedar or'to make pencile of that desired quality from any but the top grade of selected western incense cedar'. One of the proposed treatments for pencilwood, which has been used extensively on slats made from incense cedar, `is animpregnation with paraffin wax. This stiffens the spring wood but does not appreciably lubricate the denser summer wood, and, accordingly, it has not solved the cutting problem. When used in a ratio of 13 to 2() ounces for each 13 to 13.5 pounds of western cedar (enough to make 6 gross of pencils) the spring wood cuts more easily without tearing but the wood becomes hydrophobic and diiculty is encountered in gluing andV lacquering. At much lower concentrations, paraliin wax does not give suicient improvement to the cutting `characteristics `of western cedar, especially of the lower grades of irregular grain to make the lower grades useful in` good pencils.

Paraflin wax is not useful in Kenya cedar pencil slats,

ting of this relatively brittle wood. The artn paraln suitable for making pencils.

impregnation of Wood is too voluminous to require specific citations here.

Another treatment which rhas been proposed is the iinpregnation of wood vwith polyethylene glycol of molecular weight near 2000-3000 `(melting point about` 52 C.:). Thus, .Kollek et al. disclose, in U.S. Patent 1,942,146, the treatment of -wood with a dilute aqueous solution of such ,a polymerization product of ethylene oxide, and they note that the so-iinpregnated wood is softer, after drying, and easier to cut than the original. The board which wastreated was Vnot identified asto species of wood. Jt-.may -well be true that some woods will cut more easily :iftheyare softened, but it is not true of woods which are A Thus, ithas `been found .that :softeningagents tend to make the spring wood of western ,incensecedar more compressibleand more prone totear "-when cut, and that such an effect actually aggravates rather than eases thecutting problem. It has also been found that the lubricant needed to improve the cutting qualities of Kenyacedar should not exert fmuch, if any, softening effect.

. lgFrom the foregoing and related reasons it is desirable, and; it is 'the principal object of the present invention to provide a Vmethod for the modification of pencilwood iso that thel aforementioned problems `are overcome. A special object is to provide a treatment to overcome the t problems ,peculiar to the manufacture of high quality .pencils .fromheartwood or from sapwood of western incense-cedar .and to make it possible to produce pencils of substantially equal quality from grades of that wood which cannot be used either when untreated or `when `treated 4in the ways which have been proposed hereto- ,-foiee.V quality pencils,4 equal to those made from eastern red cedarfrom woods previously deemed unsuitable for such purpose. Yet Vanother object is to provide a method for minimizing the difference between the cutting qualities of` spring and summer woods of various species, to render `them more broadly usefulV in the arts. Related objects may appear from the following description of the present iinventrion.

According to the invention, the cutting qualities of `wood are improved, without softening the wood, by av kmethod which comprises subjecting the wood to a full -cellimpregnation yprocedure using a solution of l to 25 percent concentration by weight of a water-soluble poly- Vethylene glycol, or a water-soluble ether or ester thereof,

which glycol has a melting point of at least 60 C. (molecular weight at least 6000, and preferably from 8000 Vto.12,000), vin a medium of water or other polar, watermiscible solvent, and then drying .the wood slowly. The kfibers of wood so-treated are permanently swollen, due to the presence therein of from 2 to 50 percent of the polyglycol. The Vwood cuts more easily due to the lubricating effect of the polyglycol, but is not softened by the treatment. With Kenya cedar pencilwoodY and with some other woods for other purposes, the polyglycol treatment with high molecular weight polyglycol is adequate to overcome the problem. (The polyglycol treat- -ment of various woods including Kenya cedar pencilwood forms the subject of a concurrently iiled application, .Serial No. 426,572, now abandoned.) lTo make high iquality'pencilwood from western incense cedar, however, V-more vis required than the polyglycol treatment if the `iseveral problems discussed above are to be overcome. Hence, vin a preferred embodiment, the invention involves .a multi-,step treatment of western lincense cedar, to be described more fully later, comprising a step of impregnation '.with .parainv anda step of impregnation, as above described, with aqueous polyethylene glycol, to provide l to6 (preferably-y 3 to 5) percent .by-weight Aof paraffin yand from l to l percent (preferably 2 -to `6r) by weight of rthe polyglycol, based on the weight of the air dry wood, Such a treatment stiffens 'the springwood, swells 4.and lubricates all the fibers without softening them,

Related objects include the provision of highk 4 minimizes the differences in cutting qualities of spring and summer wood, and so nearly equalizes the properties of sapwood and heartwood, that all of the treated product is equivalent to the highest grade of pencil wood.

When the treatment is yapplied to western incense cedar pencilwood there is considerable latitude possible in the sequence and conditions.y of the treatments. The wood, usually after aging, is 'rst cut into slats `|,which` are conventionally about /l inch thick, 7 1A; inches .long and of a width from 3-ply to 8-ply, i.e., wide enough `to make halves of from 3 to 8 conventional Ihexagonalpencils. Because of the desire for a red cedar color, the slats are stained in an aqueous dye bath using a full cell impregnation procedure. .Excess liquid'is drained from the slats, and they .are dried slowly, over Vthe course of 4 to 15 days or more, 'to prevent warping and to reach a residual moisture content near or below 10 percent. In a preferred sequence-of operations, the driedV slats, preferably while still warm, are dipped in ory swabbed with molten Vparaffin or anV aqueous paraHn emulsion so as'to leave from 2 to 5 percent byweight of parain adherent to the wood. The slats are returned to Van ovenor kiln and held for from 3 to 6 days at a temperature slightly .above the melting point of the paraffin, Whichbecomes .over a period of 4 to 20 days and are ready for use in kmaking pencils.

In an alternative sequence of operations, thepolyglycol impregnation precedes-that with paraffin. Since the polyglycol Yis absorbed in .proportion to the woody fiberpresent, and Yis accordingly presentin greater ,concentration per unit volume in the .denser summer wood than inthe -spring wood, it is `considered undesirable to effect initial dyeing or staining of the wood by Vputting the coloring matter in a polyglycol solution. v Such a practice has the disadvantage of coloring the dense Wood more heavily If the wood hasv been given a staining treatment before the 'polyglycol` treatmenhya Vdeeper shade without undesirable striations may-tbe achieved by adding dye to the polyglycol solution, and such supplemental dyeing may be done eitherbefore-or after the parain treatment. When the parain is applied from aqueous emulsion, the emulsionniay contain dyefor a lsupplemental coloring treatment if desired. Examination of the treated wood reveals that the paraffin wax is found almost exclusively in the former `voids or inacropores of the spring wood, and is not found inthe lwoody tissue. It is also noted that, regardless of whether yparaffin is present inthe wood during Vthe treatment with polyglycol solution, the polyglycol is found `.only `in vthe woody tissue which it apparentlyy enters .through micropores,` and, as noted above, is distributed vtherein in .proportion to the density of the woody tissue. Thus, maximum lubrication is available where most needed, in the denser summer wood. selective .distribution ofthe two agents is believed tobe due to the non-polar character of the parafn andthe polar nature of the Vpolyjglycol.

In view -of -the hydrophobic nature of `Vparan wax, it was surprising that the 'present two-step -process could becarried out successfully, and especially soV that the best results are obtained when western incense cedar pencil slats are treated `with paraffin before theyare treated with the aqueous polyglycol. Only a Vsmallproportion of the rparaiinis displaced from thewood by afsubsequent impregnation with aqueous polyglycol, confirming the observation noted yabove that the two agents 2do notcomplete for the same position in the wood. The uniformity of cutting properties of the-treated wood indicates further that each treating agent is very selective 'as toits site in the wood, since such -results -would'inot '19@ Qbtaiued .ifeach agent merelyoccupied a-portion of anemona.

the same type of sites in a piece of pied by the other agent. p

The annexed drawing presents, as Fig. `1, a diagrammatic representation of the processes of the invention, and, as Fig. 2, a pencilwood slat having paralln wax distributed primarily through the macropores of the spring wood and the described polyglycolcompound impregnated more heavily in the dense summer wood than in the lighter spring wood, its distribution being proportional to the amount of Woody ber present. Y

The following examples illustrate the practice of the invention and demonstrate the importance of the several limitations as to agents for and conditions of the treatment.` l

wood as those occu- Example 1 l Western incense cedar pencil slats were impregnated with aqueous solutions `of various concentrations ofvpolyethylene glycols of various molecularA Weights. Impregnation was 4eected by `immersing the slats inthe treating solution in a closed vessel, reducing pressure `on the vessel over the liquid until bubbles ceased to escape from the wood, thenletting theslats stand overnight n the solution under atmosphericor superatmosplieric pressure. The slats were so thin (about 46 inch) that this treatment effected full cell impregnation of the wood. The slats 4were drained free from adherent liquor and were oven dried. They Weremthen conditioned at 80 F. in' air at 60 percent relative humidity, to constant weight. The cutting characteristics of each batch of the treatedwood were noted, and the results are tabulated below. "I i Polyethylene glycol Weight Average Cutting Properties of Wood percent percent Molecular in Solu- Weight` Weight tion Pickup in Wood none rittleshavings; springwood comc presses and tears. 1.0 2.3 No noticeable change. 2.0 e 3.6 Verylittle change. 3. 5 6. 5 Slight improvement, wood softened 10. 21.8 Cuts very easily, -but Wood too soft. 15.0 1 Y 33` Too soft and sticky.

4. 0 Improved, but soft. v 12.8 Guts easily, fbut soit and cheesy. 20 1 i300 c o. 35 64. 4 Excessively soft. 50 95.5 Do. 5 6.4 }Defim'te improvement; springwood 10 15.6 causes knife to drag slightly. 19.5 Much improved. Y

. 25. 2 Very good, approaches eastern cedar.

33.4 Excellent, no softening. 41.4 Do.

,56.4 Do. 2 5.3 Much improved, but some tearing.

'3.5 9:3 `Very goed.

. 5 c 12.3 t Closest to red cedar in properties.

7 21. 2` Very good. 10 `26.4 Very good, especially sapwood. 20 46,3 Good; possibly too easily eut.

It is noted that,` using polyglyCOl Solution asllh Onlylmf n Melting Freezing Polyethylene glycol, average molecular weight point point Nota-The average molecular Weights andthe `melting or freezing points are those determined and reported by commercial producers of such materials` n the United States. The products trom'different sourcesdiier slightly in molecular Weight distribution and apparent freezing points yare generally lower than melting lpoints due `to supercooling, but spot cheeks of the several products arein close agreement with the mauufacturers data given above. t t t.

It is apparent that, for pencil making, the treatment of Western incense cedar withhigh molecular Weight poly-` glycols effects a considerable improvement in the cutting qualities of thewood, but that there remains a problem in Vcutting the springwood without tearing it unless a very` high proportion of the glycol is used. While the wood is not softened bytheupreferred high molecular weight polyglycols, neither is it stiiened, and some stiffening is desirable `with western cedar, especially the sapwood of that species, when the `wood is to be used in pencil manufacture.`

Example 2 Previously dyes and dried incense cedarpencil slats were surface daubed with molten paraffin Wax vat a dosageV of 8. ounces of parain wax for each 6 gross of pencils (about 13 pounds of wood). This represents about 4 percent of paraiiin wax, based on the weight of wood. The so-treatd slats were heated in a kilm at a temperature above the melting point 'of the wax for 5 days. The paraffin v,became distributed uniformly through the wood, but the treatedwood did not cut easily, and shavings therefrom were brittle. The cut surfaces appeared dull, and'somewhatrough, incontrast to those of eastern red cedar. Some 'of the paraffin treated slats were subjected to full cell impregnation with an aqueous solution of a highmolecular weight polyethylene glycol, in the manner described in Example l. After impregnation and drying, the slats had the cutting propertiesuof` eastern red cedar, showing a surface sheen on the smooth'` cut surfaces, and giving a coherent curled shaving. There were no noticeable differences between the ease of cutting through `the springwood and the summerwood. These samples met the standards for top grade pencilwood.

Example 3 A` mill` run rwas madeto produce enough pencil slats for 2000 gross of pencils. Western incense cedar was cut into blocks 3 x 3 X 7% inches, and these were cut parallel or tangent to the annual rings to form llat slats about 1%6 inch thick. Successive slats from each block were c separated into two lots of slats of as nearlyequal qualpregnant, no satisfactory improvement A-for pencilwood purposes is obtained with glycolswhose molecular weight is appreciably below 6000. `All lower molecular` weight materials soften the :Wood and, as has been described, such a change is undesirable because it aggravates the problem of cuttingthespringwood and the undesired tearing is" `obtained with` resultantroughness. In the testsfreportedabove, all of the' polyethylene `glycols tested showedapermanent swellingeiect on the Wood. c

In addition to the minimum molecular Weight limitation derivable from the foregoing table, the `useful polyglycols can be `identified by their melting points, in accordance with` ythe `following table 4.which `lists the .melting p tfand` reeZing point ranges oftheseveralsuch glyity as possible. After dyeing, both lots WeretreatedA with about 4 percent by weight of paraffin waxas `described in Example 2. Thereafter, the'slats from one lot were given a fullmcell impregnation using a 2 percentsolu- .tion in water of polyethylene glycol `of molecularweight about 9200 and melting point near 64g4 C. After impregnation overnight and slow drying (15` days), the `glycol impregnated slats contained about 3.5 percenteach of paraffin wax and' the polyglycol. Both lots of slats, containing equal portions of each of several `grades of wood, based on established grading practices in `the trade, Were shipped to a pencil factory where they were used in parallel runs on identical equipment to make wood cased pencils. The slats which had received the dualV treatment with parain Wax and with polyglyc-olwere made into 1000 gross of pencils in 10 hours less time than was required to makera likev number of pencils fromthe slatstreated with' paratlin only. In addition, there were only 1,0` percent las many rejected' pencils (for any-i cause)l in the lotV made from` wax and polyglycol treated Wood as inthe lot from parafn treated wood. The pencils from the waX andpolyglycol treated wood all were. of top quality, regardless of the grade classification of the` wood prior to impregnation, while theronly top grade. pencils whichY were made from the wood treated only with parain Wax were those from wood which would have' been classied as of the highest quality before the wax treatment.v Hence,rthe dual treatment of the present in-` vention not only shortened the time required to make the pencils and reduced the number of rejects, but also gave pencils of consistent high quality.

pine, redwood, cypress, Douglas fir, western hemlock and even such reformed wood products as berboard.

There may be used, instead. of the Adescribed polyethylene glycols, aqueous, alcoholic, or acetone solutions of the ethers` or esters of suchglyools. Thus', the monoand: di-laurates, oleates. and stearatesl of polyethylene glycolof molecular weight of 6000 orY higher have been found. to give a satisfactory degree of permanent swelling to .wood when applied from solution in water or a watermi'sciblevsolventwsuch as ethanol' or acetone, and `to improve the'cutting properties of 'the wood, and this is true whether such impregnation follows or precedes the treatment withpar'aii wax. Similarly, such ethers of .the

polyglycols have beenV found useful'as the mono-allyl ether, the mono-sec. butylphenyl ether and the monoethyl etherf' Whenfany ofV the polyglycol compoundsV suggested above isl being used, and it is`desired` to 'increase the .hardness'ofthe wood,'there maybe added to the solution ofthe polyglycol a wood hardener'which is soluble in thesamernedium. Examples of suchhardenerjs lare the aldose" and ket'ose "sugarsfsuch asV glucose,`fr uctose and lactose, and any of'several water-soluble-resins, especially those which. tendtof'harden during exygosure to enough heat 't'o dry the'impregnat'e'd/wood. Among theresins and polymers which may be used.. are water-soluble phenollformaldehyde resins, water-soluble ureaor melaminealdehyde .resins, toluene sulfonamide-aldehyde resins, and water-soluble polymers, such as. polyacrylamide, polyacryliciacid, polyvinylalcoholy and polyvinylsulfonic acid.

1 The following. examples illustratethez effect of typical hardening .agents when used together withapolyethylene glycol.. .'Inthese examples, no paraffin Vwax treatment Vwas used,..asf.it is desired only to demonstrat'ethe eifect'of f the hardened Example i jPenci-l' slats of incense cedarsvapwood and heartwood andL of. Kenya cedar were impregnated in similar manner mixedv aqueous solutions of varyingv composition .containing polyethylene glycol (mol wt. 6000) and a phenolformaldehyde resin` as -hardenen The resinwas madefrom'arn'ixture consisting of 349 grams 3.7lmols) phenol, 550 cc. (71.42 mols) 37 percent aqueous formaldehyde solution, 17.5 gramsl sodiuml carbonate, 17.5 grams alpha-protein and 3 grams added water, which was cookedunder reflux to a'viscosity of 50 centipoises. The following table `shows' the composition of lthe treating solutions' in percentage by weightl and theincrease in'dry weight ofthe treated1samp1es z y Solution Percentl Gamin Weight. I

ercentf Percent Sapwood lieartwood. Kenya 5 Polyglycol' Resin' 1 K 5; o "1.8 20.0 17. ov 6.o 7. 2. 5V 17. 0 18.0 5: 0 10. 0 l 3, 5 27. 0 33. 0 7. 0 15,'0 7. 5 06. 0 47; 0` 14. 0

All ofthe treated samples s howedexcellent cutting properties, superior to the `untreated wood, except the incense cedar sample containing 66.0 percent added solids, which 15 was too hardand gritty, for` good cutting.

b Example To show the hardening eife'ctof dextrose, test blocks of incense cedar sapwood. and heartwoodwere yimpregnated with percent aqueous solutions of polyethylene glycol (mol wt. 9000) to which varying amount's'ofcommercialdextrose were added. The samples-were weighed toA determine gain in weight, and their cutting properties testedg'wi'th results as ygivenY in the following table.l

v Percent Gain in vPercent; Weight Cutting' No. 'Dextrose Properties Vin Soin.`

' Sapwood Heartwood 1.0 37.0' 21.0' 'Slight1ysoft. 2.10 40.0 34.0 Excellent. 3. 5 43. 0 25.0 Very good. 4 5. 0 47.0 33. 0 Slightly too hard'.

Incense cedar, when impregnated with a 15 percent solution of polyethylene glycol (mol wt. 9000*) lis some1 what'too soft forl best .cutting properties. When the treating solution is modified by addition of small amounts .of dextrose, as above, the hardnessof incense cedar impregnated with the modied solution is increased. Of the above samples, No.` l is slightly toosoft, Nos. 2 and 3 have a degree of hardness giving desirablev cutting properties, and No. 4 is slightly toohard. v

The parainwax which is used in the treatment of wood according to the present invention is any suchwax having a melting pointi tif-120- F. (49 C.) .or4 higher. It may be applied, asdescribed, from themoltencon'- dition, or it may be used in the form of an aqueous emulsion, either type of application being followed by heat treating the wood' to causethe wax to melt and to become uniformly distributed through the wood in which it* is found thereafter to be'principally in the springwood.V The paralin'wax treatment ispreferably employed before the wood has been impregnated with theV highmolecular weight polyglycol, but it has been found that the cutting properties -of' western incense cedar pencilwood are improved to substantially the same Vextent when the parailn wax treatment follows the treatment with the polyglycoll The specific conditions employed in the successive treating step-sof the invention do not appear to be critical Asojlong as the paraflin wax is so applied'as' to become sub? stantially uniformly distributed througlrthe wood and the. polyethylene glycol is used in anyof the well known full cell impregnation procedures;4 When applying theV invention to western incense cedar pencil slats it' isv iniportantV that thel wood be dried very slowly after any im'- -pregnation withV an aqueousv solution, to prevent warping and to prevent the'escaping waterfrom Hcarrying itssolute to the surface of the wood. Similarconsi'derationsirecornL mend a slow dryingprocedure when the invention is apL plied 'to"woods othery than' incense cedarf'which tend: to warp or4 todisplayV raised grain .after treatment with aqueous rn'edia4 'l i The-amount' ofparan wax and ofpolyglycol` needed l to ligive the'maximum reductiony in the differences be'- tween cutting propertiesof spring' and summer rwood varies somewhat with the species being treated. The amount of paraffin Wax which can be used advantageously seldom exceeds 6 percent of the weight of wood, and is often as little as 1 to 2 percent, though there are uses for various Woods in which larger amounts of parafn are not harmful. The amount of polyglycol varies morewidely, being most frequently in the range from 2 to 10 percent, with amounts up to 50 percent being acceptable in the case of some light, brittle woods.

I claim:

1. The method for diminishing diiferences between the cutting characteristics of spring and summer wood without materially softening the wood, which comprises the steps of (A) distributing through the wood from l to 6 percent of its weight of parain wax having a melting point of at least 49 C.; and (B) subjecting the wood to full cell impregnation with a water-miscible solution of from 1 to 25 percent by weight of a compound from the group consisting of polyethylene glycol, having a molecular Weight of at least 6000 and a melting point of at least 60 C., and the water-soluble ethers and esters thereof, and drying the .so-impregnated wood slowly.

2. The method claimed in claim 1, wherein the wood subjected to treatment is western incense cedar.

3. The method claimed in claim 1, wherein step (A) precedes step (B).

4. The method claimed in claim 1, wherein step (B) is carried out using a water solution of from 1 to 5 percent concentration by weight of polyethylene glycol having a molecular weight of from 6000 to 12,000 and a melting point of at least 60 C.

5. The method which comprises distributing substantially uniformlythrough Western incense cedar pencil slats of polyethylene glycol having a molecular weight of from 6000 to 12,000 and a melting point of at least C., and drying the so-impregnated slats slowly so as to avoid warping, thereby to minimize differences between the cutting characteristics of spring and summer wood.

6. The method of diminishing differences between the cutting characteristics of spring and summer Wood without materially softening the wood, which comprises the steps of impregnating the wood with paratlin wax so that the wax enters the voids and pores thereof, impregnating the wood with an aqueous solution of polyethylene glycol having a molecular weight of from about 6000 to 12,000 and then slowly drying the so impregnated wood.

References Cited in the le of this patent UNITED STATES PATENTS 997,275 Crocker July 11, 1911 1,699,635 Smith Jan. 22, 1929 1,942,146 Kolleck et al. Jan. 2, 1934 2,386,828 Wilcox Oct. 16, 1945 2,469,049 Miller May 3, 1949 FOREIGN PATENTS 831,524 France June 7, 1938 OTHER REFERENCES Wood Preservation, B. Van Groenou, Holland, 1951. (Copy in Div. 25.) 

1. THE METHOD FOR DIMINISHING DIFFERENCES BETWEEN THE CUTTING CHARACTERISTICS OF SPRING AND SUMMER WOOD WITHOUT MATERIALY SOFTENING THE WOOD, WHICH COMPRISES THE STEPS OF (A) DISTRIBUTING THROUGH THE WOOD FROM 1 TO 6 PERCENT OF ITS WEIGHT OF PARRAFIN WAX HAVING A MELTING POINT OF AT LEAST 49*C.; AND (B) SUBJECTING THE WOOD TO FULL CELL IMPREGNATION WITH A WATER-MISCIBLE SOLUTION OF FROM 1 TO 25 PERCENT BY WEIGHT OF A COMPOUND FROM THE GROUP CONSISTING OF POLYETHYLENE GLYCOL, HAVING A MOLECULAR WEIGHT OF AT LEAST 6000 AND A MELTING POINT OF AT LEAST 60*C., AND THE WATER-SOLUBLE ETHERS AND ESTERS THEREOF, AND DRYING THE SO-IMPREGNATED WOOD SLOWLY. 